I'll hold the candle

A phrase meaning "I will assist but not actively participate." This is derived from a period where apprentices would hold a candle for their master to work. Related to the phrase "couldn't hold a candle", when a person is being described as being so inadequate that they were not fit to assist.

John: "The engine is shot. I'll have to take the whole thing apart to figure it out."
Melissa: "I'll hold the candle."